The present invention relates to a charged particle irradiation apparatus for irradiating irradiation targets with charged particles. The charged particle irradiation apparatus is applied for various purposes such as remedies of cancer, sterilization of foods, improved breeding of plants, nondestructive inspection of machine structures, and others.
In accordance with a conventional charged particle irradiation apparatus, a charged particle beam has been enlarged by a scatterer and the like in order to obtain a wide irradiation area, of which dose distribution is uniform. For example, in order to remedy a cancer by irradiation with protons, heavy particles, and the like, it is necessary to enlarge the charged particle beam having an energy of approximately 230 MeV at maximum up to approximately 20 cm in diameter in a case of protons. Then, the enlarged charged particle beam is formed in a shape of the irradiation target, an affected part, by a collimator. Subsequently, the affected part is irradiated with the charged particle beam.
The Japanese Utility Model Publication No. Hei 5-40479 (1993) taught a method that, by employing a Wobbler method of scanning the charged particle beam with two units of deflection magnet, the charged particle beam is enlarged by passing through a scatterer, which is provided in the upstream or the downstream of the two units of deflection magnet.
However, in accordance with the prior art, both the two units of the deflection electromagnet were arranged inside the irradiation apparatus, which had caused a problem of increasing the size of the irradiation apparatus. The increase in size of the irradiation apparatus necessitates a larger rotation radius of the rotation gantry, which makes the whole devices larger, and causes a problem of an increase in construction cost.
The Wobbler method shows a property that the longer the distance between a focus position of the Wobbler's deflection electromagnet and a position of the scatterer gets, the wider the lateral dose falloff (half-shadow blur ) of the shape of the charged particle beam formed by the collimator becomes.